Widespread use of the digital still camera and the video movie camera that use the solid-state image sensor results in a strong demand for smaller imaging devices. In order to satisfy such a demand for smaller imaging devices and to further improve portability, the so-called “collapsible lens barrel”, which retracts into a camera body when performing no image shooting, has been widely used. The length of the collapsible lens barrel is changed by a motor rotating a rotational barrel to move an optical imaging system in the optical axis direction.
As for conventional collapsible lens barrels, if any impact is applied thereto, for example, due to a fall with the barrel being extended, any force acting on cam pins is converted to a force that rotates the rotational barrel, so that the rotational barrel might be rotated. Where only the rotational barrel is rotated with the motor for rotating the rotational barrel being stopped, load is applied to a mechanism used for extension, including gear trains, for example, so that in some cases, gears might be damaged.
There have been proposed some structures for locking rotation of the rotational barrel, for example, in order to prevent the gears from being damaged when any impact is applied to the lens barrel. For example, in Japanese Laid-Open Patent Publication No. 2003-279827, cam grooves are each shaped to have a planar portion perpendicular to the optical axis in such a manner as to cause no force to be generated in the direction of rotating the rotational barrel, thereby inhibiting rotation of the rotational barrel. However, in the case of the structure as described in Japanese Laid-Open Patent Publication No. 2003-279827, the effect of inhibiting the rotation of the rotational barrel is limited, and there are large gaps between the cam grooves and the cam pins, resulting in a problem where image blur might occur.